unjar.sh

#!/bin/sh
# Dependencies: sed, grep
# 
# Usage: unjar FILE [DEST]
#
# - DEST must not already exist (won't overwrite existing contents);
#   path to DEST will be created.
#   TODO: add overwrite option
#
# - If DEST is not provided, defaults to a subdirectory in the current
#   working directory that will be named after FILE without the extension.
#   Ex: unjar foo.jar  # foo.jar extracted to ./foo
#
# - If DEST is provided, the path will be created and the jar will
#   be extracted into it.
#   Ex: unjar foo.jar /a/b/c  # foo.jar extracted into /a/b/c
#   TODO: add option to extract into final path component based on
#         the filename
#         Ex: unjar -X foo.jar /a/b/c  # foo.jar extracted into /a/b/c/foo

error() {
  echo "Error: $@"
  echo "Usage: $(basename $0) FILE [DEST]"
  exit 1
}

# return the file name (including extension) without any path components
basename() {
  printf "$1" | sed 's/^.*\///'
}

# returns name without an extension (must already be a basename)
dropext() {
  printf "$1" | sed 's/\.[^.]*$//'
}

strip_trailing_slashes() {
  printf "$1" | sed 's/[/]*$//'
}

# If empty arg, return .
# If nothing but slashes, return /
# If no slashes after stripping all trailing slashes, return .
# Otherwise, return everything up until last path component
dirname() {
  if [ -z "$1" ]; then printf '.'; return; fi
  if ! $(printf "$1" | grep -q '[^/]'); then printf '/'; return; fi

  local s="$(strip_trailing_slashes $1)"
  if ! $(printf "$s" | grep -q '/'); then printf '.'; fi

  printf "$(strip_trailing_slashes $(printf $s | sed 's/[^/]*$//'))"
}

if [ -z "$1" ]; then error "missing filename"; fi

FILE="$1"
if ! [ -r "$FILE" ]; then error "can't read file: $FILE"; fi

# Need to know full pathname for the file so that it can be
# extracted after changing directory to DEST.
PATHNAME="$(printf "$(cd "$(dirname "$1")"; pwd -P)/$(basename "$1")")"

# Need to cd to DEST directory before extracting the jar file.
DIR="${2:-$(dropext $(basename $FILE))}"
if [ -e "$DIR" ]; then error "target directory already exists: $DIR"; fi
mkdir -p "$DIR" && cd "$DIR"

jar -xf "$PATHNAME"